In recent years, “water main direct-pressure” type flush toilets, in which flush water is supplied directly from a water main, have become more prevalent. In this type of water main direct pressure-type flush toilet, the toilet is generally flushed in a sequence whereby water is spouted from a rim spout at the top of the bowl portion, then from a jet spout at the bottom portion of the bowl portion, then a second time from the rim spout, each for a predetermined time. Because water main direct pressure-type flush toilets do not require a tank for holding all of the flush water for a single flush, they have the advantage that they can be made more compact, but on the other hand have the problem that it may be difficult to supply flush water at an adequate flow rate in localities with low water main pressure, making them difficult to install.
Moreover, the duration of water spouting from the rim spout or the jet spout when flushing the toilet is generally set to be such that the amount of flush water expelled is sufficient even when a water main direct pressure-type flush toilet is installed in an locality with relatively low water main pressure. The problem therefore arises that the amount of flush water expelled is excessive when a water main direct pressure-type flush toilet is installed in a normal water main pressure locality.
U.S. Pat. No. 2,874,207 (Patent Citation 1) describes a flush water supply device for a toilet. In this flush water supply device, a pressure sensor or flow rate sensor is disposed on the water supply path to the rim spout, and a flush water spouting time is set based on values detected by the sensor. In other words, an appropriate volume of flush water can be supplied by using a long spout time in localities with low water main pressure, and a short spout time in localities with high water main pressure.    Patent Citation 1: U.S. Pat. No. 2,874,207